I don't think that's true. Verizon to Verizon and AT&T to AT&T calls are free, however, I believe when calling Verizon to AT&T or any other carrier, it counts against your allocated minutes or texts. Of course if you have unlimited, then it doesn't matter.

So more appropriately, using Facetime or iMessage between iOS devices is free of charge..but using the standard SMS application or making phones calls is not free unless you are on the same provider and that provider provides that option..